Update README.md

Adding train-eval-index to make it easier to validate models using the HF model evaluator.

README.md

@@ -13,6 +13,18 @@ task_ids:
 - extractive-qa
 - closed-domain-qa
 - open-domain-qa
+train-eval-index:
+- config: plain_text
+  task: question-answering
+  task_id: extractive_question_answering
+  splits:
+    train_split: train
+    eval_split: test
+  col_mapping:
+    context: context
+    question: question
+    answers.text: answers.text
+    answers.answer_start: answers.answer_start
 ---
 
 ![bert_image](https://thumb.tildacdn.com/tild3433-3637-4830-a533-353833613061/-/resize/720x/-/format/webp/germanquad.jpg)